1. Field of the Invention
The present invention generally relates to a mode converter and a microwave rotary joint with the mode converter, more particularly to a mode converter that converts microwave signals of a TE01 circular symmetric mode and a microwave rotary joint that transmits the microwave signals of the TE01 mode.
2. Description of the Prior Art
High frequency microwave rotary joints are mainly applied to radar systems or terminal joints of cables, and therefore the microwave rotary joints are important waveguide structures. Hence, to design a high frequency microwave rotary joint shall think about a propagation efficiency and a suitable band scope, and it is more important that the rotary joint must be with a propagation characteristic not related to swirl.
With reference to FIG. 1, which illustrates a schematic view of a typical microwave rotary joint. As shown in the figure, the microwave rotary joint 100 includes a fastening end 120, a swirl end 140, a middle channel 160, and two mode converters 180, wherein the dimensions and shapes of the fastening end 120 and the swirl end 140 are determined by a system, which is connected to the fastening end 120 and the swirl end 140, usually the fastening end 120 and the swirl end 140 are rectangular waveguides, two ends of the middle channel 160 are respectively connected to the fastening end 120 and the swirl end 140 and shaped as circular, a swirl structure of the microwave rotary joint 100 is disposed at the middle channel 160.
As aforesaid, the structures of the fastening end 120, the swirl end 140 and the middle channel 160 are different. For this reason, the operation modes to the fastening end 120, the swirl end 140 and the middle channel 160 are different; consequently the two mode converters 180 must be respectively disposed at two positions, one of which is between the fastening end 120 and the middle channel 160, the other one is between the swirl end 140 and the middle channel 160, so as to proceed conversion of waves for a better couple effect. Further that, the conversion types of the mode converter 180 are determined by the modes of microwaves, and the microwaves are transmitted by the microwave rotary joint 100.
To decide the operation mode of the middle channel 160 is the most important. To begin with, the transmitting modes of microwaves inside the middle channel 160 must be circular and symmetric and without the influence of the swirl, for examples, circular TE01 mode, circular TE11 mode, etc. The next, the swirl structure of the microwave rotary joint 100 is disposed at the middle channel 160, and a seam must be at where the swirl structure is. For those transmitting modes suitable to the middle channel 160, the circular TE01 is only with traverse surface currents and not without vertical surface currents, which is along the axial direction of the column middle channel 160, the surface currents may not be easily cut off by the seam. Accordingly the circular TE01 mode is acknowledged to be a preferred choice to the microwave rotary joint.
Thereafter, to effectively convert the microwave signals from the swirl end 120 or the fastening end 140 to the microwaves with the circular TE01 mode and transmitted in the middle channel 160 becomes an important issue for people skilled in the art.